Valve actuation in an internal combustion engine is required for the engine to produce positive power, as well as to produce engine braking. During positive power, intake valves may be opened to admit fuel and air into a cylinder for combustion and exhaust valves may be opened to allow combustion gases to escape from the cylinder.
For both positive power and engine braking applications, the engine cylinder intake and exhaust valves may be opened and closed by fixed profile cams in the engine, and more specifically by one or more fixed lobes which may be an integral part of each of the cams. The use of fixed profile cams makes it difficult to adjust the timing and/or amounts of engine valve lift needed to optimize valve opening/closing times and lift for various engine operating conditions (often referred to as variable valve actuation (VVA)), such as different engine speeds.
One method of adjusting valve timing and lift, given a fixed cam profile, has been to incorporate a “lost motion” device in the valve train linkage between the valve and the cam. Lost motion is the term applied to a class of technical solutions for modifying the valve motion dictated by a cam profile with a variable length mechanical, hydraulic or other linkage means. In a VVA lost motion (LM) system, a cam lobe may provide the “maximum” (longest dwell and greatest lift) motion needed for a full range of engine operating conditions. A variable length LM system may then be included in the valve train linkage, intermediate of the valve to be opened and the cam providing the maximum motion, to subtract or lose part or all of the motion imparted by the cam to the valve.
Unfortunately, although LM systems are beneficial in many aspects, they are also subject to several drawbacks. For example, in many current VVA LM systems, each valve in the engine requires its own hydraulic switching components (e.g., a so-called high speed solenoid valve) and associated electronics, resulting in added cost and complexity.